Call the registrar's office at the college or university, or the counselor's office at the high school the person reportedly graduated from. Tell the representative that you are calling to verify that he completed his degree. Submit the person's name, birthdate, Social Security number and reason for the request (e.g., employment). The representative will verify if he graduated from that school.
Request an official transcript from the person. If she graduated, she can request an official transcript from her school. The transcript will state whether the person graduated from the institution. There is a fee for this service, which ranges per institution. An official transcript is stamped and sometimes sealed in an envelope. The transcript can be sent directly to you. You can also request an unofficial transcript, which is often cheaper. Unofficial transcripts are stamped "Unofficial."
Request that the person show you his diploma certifying that he graduated from the institution. Most graduates will have a diploma.